[MCA] Remove SM.hasNext() call in FetchStage::execute.
[MCA] Remove SM.hasNext() call in FetchStage::execute.

Summary:
This is redundant, as FetchStage::getNextInstruction already checks this
and returns llvm::ErrorSuccess() as appropriate.

NFC.

Reviewers: andreadb

Subscribers: gbedwell, llvm-commits

Differential Revision: https://reviews.llvm.org/D52642

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@343555 91177308-0d34-0410-b5e6-96231b3b80d8

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